LAUSR

Abstract Polycrystalline films La1-xCaxMnO3-δ (LCMO) deposited on (001) MgO substrates for three different Ca concentrations (x = 0.67, 0.75, 0.85) were studied by Raman spectroscopy, X-ray diffraction and scanning electron microscope (SEM). Images of the surface and cross-section (edge) of samples of all compositions were obtained using SEM with high (up to 1 nm) spatial resolution. It was demonstrated that changes occur in the morphology and the formation of preferential orientation films x = 0.75, 0.85 relative to the substrate. It was founded that with an increase in the quantity of calcium there occurs a decrease in parameter pseudocubic unit cell. We have investigated the temperature (80K-350K) dependence of the Raman spectra of LCMO films. We have shown that Raman response of polycrystalline films below 150K corresponds to the microscopic coexistence of isostructural phases, with crystallographic symmetry Pnma. Detailed analysis of spectra allows to detect the occurrence of several different local lattice distortions: structural phases that have weak Jahn–Teller or/and spin crossover induced structural distortions with distorted octahedra Mn3+O6 and symmetric or nearly symmetric Mn4+O6 octahedra and the octahedral tilts in charge-ordered manganese films LCMO with x = 0.67, 0.75 at low temperature. Our results confirm the coexistence of charge–ordered antiferromagnetic state and ferromagnetic metallic phases with the competition between super-exchange and double-exchange interactions.